Hi

Quick question;

I'm after an 8v block for my build. I have found a MK2 what looks to be an okay block but it has 16V at the end of the engine number although the guy says it definately came off an 8 valve engine...

What was the difference between the 16v and 8v mk2 pistons, did they lower compression?

Is it possible fiat fitted a 16v block with 8v parts at the factory?

Cheers,

Matt

Anything is possible. But strange indeed.

Engines and blocks are not exactly rare -- I'd walk away, myself.

as far as im aware there the exact same the blocks...just pistons and maybe crank different but I even think crank is same tbh...they just changed the internals and kept same block imo

after all its the exact same CC so bores are the same just 8 extra valves in head

Problem is its easy to buy and engine from a scrapped car, get home and find all the rings are melted in and stuck and the bores are badly worn and finished which is what we have done once now already... Maybe thats not common and just bad luck but we dont really want it happening again

The reason I am interested in this block is because its already stripped, fairly cheap and I can see the bores which look very good compared with the other 1242 we now have and the 1108 seicento engine, obviously we will fully strip and inspect but its a far better starting point.

The reason im slightly worried about it being 16v pistons is because I have read on this forum they lower compression. Im not sure how this is done because I searched but I coudlnt find a picture of said piston... I would hazard a guess it would be easy to identify a 8V piston as it would have 2 slots for valves whereas a 16V piston would have 4 slots...

Are all punto 1242 pistons slightly dished with two cut-outs from valves? The 1108 ones we removed from the seicento are flat top.

If anyone has any pictures kicking around to explain the above that would be great!

Cheers,

Matt

luckily I keep pics from when I mess around with engines haha

8v piston (this is the one I was telling you about on PM)



16v pistons



8v (left) vs 16v (right)

Hi Brin,

Awesome pictures! Thank you very much for your help fully clear now!

Cheers,

Matt

Yeah, 16v pistons will lower compression (a lot!) so you need to use 8v rods and pistons. But difference should be clear -- 8v ones don't have the dish.

Terrific pictures, BTW.

Why do the were the 16v lower in compression out of interest? I can only think that its to do with being able to intake more air?

chrisb7777 said:

Why do the were the 16v lower in compression out of interest? I can only think that its to do with being able to intake more air?

Click to expand...

no worries glad I cleared everything up

16v pistons have a more dished crowns so the compression ratio de-creases due to the more space within the cylinder on compression strokes...you only want this for turbo convserions not for NA running engines

NA running engines you want higher compression ratios for power

lower compression de-creases th risk of detonation during boost hence why it is done also slightly retards the timing

The compression isn't lower in the 16v if you have the 16v head.

So, it's primarily the combustion chamber shape in the head that makes the difference (more of the 16v combustion chamber is in the piston, than in the 8v, where it's mainly in the head).

For n/a engines, lower compression is a bad thing, just as Brin points out.

Ahh i see, im learning!

nice to know

fingers99 I have wondered this for a while now...we use 16v pistons to lower the compression ratio of 8v engines due to the dished crowns, so will putting 8v pistons into a 16v engine be beneficial? will it give it a nice high compression and better power or will it be going a step too far? lol

I think you'll get valve to piston contact! But too high, methinks, even if you didn't.

It would be very interesting to look at the Brazilian home market engines -- I'd guess they've upped the CR further to benifit from ethanol.

in all honesty I am really curious about this...I may have to experiment and play with a 16v engine just for the sake of seeing what happens aha

I have a 16v block but its sat miles away in a workshop but from looking at pictures they aren't exactly the same - if you look for head gaskets for the 2 engines the differ ever so slightly.

if you look at these 2 pics there is probably people who know what these channels are.. 16v at top 8v at bottom, there is a hole missing on the 16v gasket in the middle and next to that one of the holes is a different shape...

Makes me think 16v cannot be used with a 8v head despite the fact they will bolt together, but i stand to be corrected.



note: they are opposite way up from each other, couldn't find 2 pics the same way round.

blocks are same, heads are different hence the need for different headgasket...because the water jackets in the 16v head will be placed different to the 8v but be fed from the same on the block...the difference in holes will just be to feed the coolant and oil to the correct sections for that specific head...obvs the galleys on the head will not be the same

Surely the only reason the piston heads are a different shape is because they are for a 16 valve head? It's all about getting the **** in and out?

I have an 8V head spare that I bought in error.

£25.00 for shipping and its yours